1. Field
This invention relates to hydrometallurgical processes for chlorinating metal sulfide materials to produce metal chlorides.
2. State of the Art
Although hydrometallurgical processes are well known, many metals are customarily extracted from their ores by smelting. For example, copper sulfide ores are normally subjected to concentration procedures, and the concentrates are then smelted to produce impure metallic copper, which is then refined to the desired purity. The sulfur values in the concentrates form gaseous sulfur oxides during the smelting phase of this overall processing of the ore.
The production of large amounts of these sulfur oxide gases, which, when released into the atmosphere, cause significant air pollution, is a major disadvantage of smelting processes. Increasing attention is being given at all levels of government to ways of eliminating air pollution, especially that caused by the venting to the atmosphere of gaseous sulfur oxides. Accordingly, the hydrometallurgical approach is being favorably considered by the metallurgical art as an alternative to the smelting of ore materials.
Among proposed hydrometallurgical processes are ones employing a chlorinating agent to chlorinate the ore materials and form chlorides of the particular metal values to be recovered, the metallic chlorides being then further processed into metal. Two major problems have been encountered in chlorination processes: (1) Large excesses of the chlorinating agent over stoichiometric have been required to effectively extract the metal values from the minerals, and, since such agents are expensive, the economics have proven prohibitive. (2) Even after the metal values have been extracted as chlorides, it has been found extremely difficult to separate the metal chlorides from the elemental sulfur released from the sulfide minerals and present in the reaction medium with the metal chlorides. Attempts to remove the sulfur by volatilization have required tempertures of over 445.degree. C. (the boiling point of sulfur), which are expensive to maintain. To date, these major problems have prevented serious consideration of chlorination as an alternative to the presently employed smelting of sulfide ore materials.